This function will calculate the distance and azimuth (referenced to True North) between two sets of coordinates on the Earth. Bearings or azimuths start with 0 degrees toward true north, 90 degrees east, 180 degrees south, and 270 degrees west (clockwise rotation).
The terminal coordinates program  can be used to find the coordinates at some distance, given an azimuth and the starting coordinates.
The shortest distance between two points on the surface of a sphere is an arc, not a line. In addition, the azimuth looking from Point B to Point A will not be the converse (90 degrees minus the azimuth) of the azimuth looking from Point A to Point B. (Try this using a string on a globe.)
Applicants will find this program helpful in determining compliance with the minimum spacing table in 47 CFR 73.207 for FM stations or 47 CFR 73.610 for television stations, or suitable allotment reference coordinates for FM commercial stations. DXers (long distance listeners and viewers) may find this program useful to help determine how far away originating stations are, if the station's coordinates are known (try the AM Query , FM Query  for radio broadcast stations in the United States, or TV Query  for television stations).
Adapted for Internet use by Dale Bickel in December 1998.
Questions on Distance Between Coordinates may be directed to Dale Bickel, email@example.com .
For more information about this function, please call the Audio Division  at (202) 418-2700.